Zoom lens system, imaging device and camera

ABSTRACT

A zoom lens system comprising: a positive first lens unit; a negative second lens unit; a positive third lens unit; a fourth lens unit; and an aperture diaphragm provided between the third lens unit and the fourth lens unit, wherein in zooming, the first to third lens units are moved along an optical axis to perform magnification change, the third lens unit includes two or more lens elements and one or more inter-lens-element air spaces, and the conditions: −7.0&lt;f 1 /f 2 &lt;−4.0 and f T /f W &gt;9.0 (f 1  and f 2 : composite focal lengths of the first and second lens units, f W  and f T : focal lengths of the entire system at a wide-angle limit and a telephoto limit) are satisfied.

BACKGROUND

1. Field

The present disclosure relates to zoom lens systems, imaging devices andcameras.

2. Description of the Related Art

Cameras including an image sensor for performing photoelectricconversion, such as digital still cameras and digital video cameras,have been required to have high resolution, and particularly in recentyears, these cameras have been strongly required to have a reducedthickness, a high zooming ratio, and capability of compensating variousaberrations. For example, various kinds of zoom lens systems have beenproposed, each having a three-or-more unit configuration of positive,negative, and positive, or positive, negative, and negative, in which afirst lens unit having positive optical power, a second lens unit havingnegative optical power, a third lens unit having positive or negativeoptical power, and a subsequent lens unit are arranged in order from anobject side to an image side. Hereinafter, the cameras including animage sensor for performing photoelectric conversion, such as digitalstill cameras and digital video cameras, are simply referred to as“digital cameras”.

Japanese Laid-Open Patent Publications Nos. 2010-237455, 2007-108398,and H10-111455 each disclose a zoom lens having the three-or-more unitconfiguration of positive, negative, and positive.

Japanese Laid-Open Patent Publication No. 2009-265652 discloses a zoomlens system having the three-or-more unit configuration of positive,negative, and positive, or positive, negative, and negative.

Japanese Laid-Open Patent Publication No. 2009-175736 discloses a zoomlens having the three-or-more unit configuration of positive, negative,and positive, or positive, negative, and negative.

Japanese Laid-Open Patent Publication No. 2009-009121 discloses a zoomlens system having the three-or-more unit configuration of positive,negative, and positive.

SUMMARY

The present disclosure provides: a high-performance and thin zoom lenssystem that has, as well as high resolution, a high zooming ratio, buthas less aberration fluctuation in zooming; an imaging device employingthe zoom lens system; and a thin and compact camera employing theimaging device.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the related art, and herein is disclosed:

a zoom lens system, in order from an object side to an image side,comprising:

a first lens unit having positive optical power;

a second lens unit having negative optical power;

a third lens unit having positive optical power;

a fourth lens unit having optical power; and

an aperture diaphragm provided between the third lens unit and thefourth lens unit, wherein

in zooming from a wide-angle limit to a telephoto limit at the time ofimage taking, the first lens unit, the second lens unit, and the thirdlens unit are moved along an optical axis to perform magnificationchange,

the third lens unit includes two or more lens elements, and one or moreinter-lens-element air spaces, and

the following conditions (1) and (a) are satisfied:−7.0<f ₁ /f ₂<−4.0  (1)f _(T) /f _(W)>9.0  (a)

where,

f₁ is a composite focal length of the first lens unit,

f₂ is a composite focal length of the second lens unit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

f_(T) is a focal length of the entire system at a telephoto limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the related art, and herein is disclosed:

an imaging device capable of outputting an optical image of an object asan electric image signal, comprising:

a zoom lens system that forms the optical image of the object; and

an image sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein

the zoom lens system is a zoom lens system, in order from an object sideto an image side, comprising:

a first lens unit having positive optical power;

a second lens unit having negative optical power;

a third lens unit having positive optical power;

a fourth lens unit having optical power; and

an aperture diaphragm provided between the third lens unit and thefourth lens unit, wherein

in zooming from a wide-angle limit to a telephoto limit at the time ofimage taking, the first lens unit, the second lens unit, and the thirdlens unit are moved along an optical axis to perform magnificationchange,

the third lens unit includes two or more lens elements, and one or moreinter-lens-element air spaces, and

the following conditions (1) and (a) are satisfied:−7.0<f ₁ /f ₂<−4.0  (1)f _(T) /f _(W)>9.0  (a)

where,

f₁ is a composite focal length of the first lens unit,

f₂ is a composite focal length of the second lens unit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

f_(T) is a focal length of the entire system at a telephoto limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the related art, and herein is disclosed:

a camera for converting an optical image of an object into an electricimage signal, and performing at least one of displaying and storing ofthe converted image signal, comprising:

an imaging device including a zoom lens system that forms the opticalimage of the object, and an image sensor that converts the optical imageformed by the zoom lens system into the electric image signal, wherein

the zoom lens system is a zoom lens system, in order from an object sideto an image side, comprising:

a first lens unit having positive optical power;

a second lens unit having negative optical power;

a third lens unit having positive optical power;

a fourth lens unit having optical power; and

an aperture diaphragm provided between the third lens unit and thefourth lens unit, wherein

in zooming from a wide-angle limit to a telephoto limit at the time ofimage taking, the first lens unit, the second lens unit, and the thirdlens unit are moved along an optical axis to perform magnificationchange,

the third lens unit includes two or more lens elements, and one or moreinter-lens-element air spaces, and

the following conditions (1) and (a) are satisfied:−7.0<f ₁ /f ₂<−4.0  (1)f _(T) /f _(W)>9.0  (a)

where,

f₁ is a composite focal length of the first lens unit,

f₂ is a composite focal length of the second lens unit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

f_(T) is a focal length of the entire system at a telephoto limit.

A zoom lens system in the present disclosure is a high-performance andthin zoom lens system that has, as well as high resolution, a highzooming ratio, but has less aberration fluctuation in zooming. Animaging device in the present disclosure employs the zoom lens system,and a camera employing the imaging device is thin and compact.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects and features of the present disclosure willbecome clear from the following description, taken in conjunction withthe exemplary embodiments with reference to the accompanied drawings inwhich:

FIG. 1 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 1 (NumericalExample 1);

FIG. 2 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Numerical Example 1;

FIG. 3 is a lateral aberration diagram of a zoom lens system accordingto Numerical Example 1 at a telephoto limit in a basic state where imageblur compensation is not performed and in an image blur compensationstate;

FIG. 4 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 2 (NumericalExample 2);

FIG. 5 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Numerical Example 2;

FIG. 6 is a lateral aberration diagram of a zoom lens system accordingto Numerical Example 2 at a telephoto limit in a basic state where imageblur compensation is not performed and in an image blur compensationstate;

FIG. 7 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 3 (NumericalExample 3);

FIG. 8 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Numerical Example 3;

FIG. 9 is a lateral aberration diagram of a zoom lens system accordingto Numerical Example 3 at a telephoto limit in a basic state where imageblur compensation is not performed and in an image blur compensationstate;

FIG. 10 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 4 (NumericalExample 4);

FIG. 11 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Numerical Example 4;

FIG. 12 is a lateral aberration diagram of a zoom lens system accordingto Numerical Example 4 at a telephoto limit in a basic state where imageblur compensation is not performed and in an image blur compensationstate;

FIG. 13 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 5 (NumericalExample 5);

FIG. 14 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Numerical Example 5;

FIG. 15 is a lateral aberration diagram of a zoom lens system accordingto Numerical Example 5 at a telephoto limit in a basic state where imageblur compensation is not performed and in an image blur compensationstate; and

FIG. 16 is a schematic configuration diagram of a digital still cameraaccording to Embodiment 6.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described with reference to thedrawings as appropriate. However, descriptions more detailed thannecessary may be omitted. For example, detailed description of alreadywell known matters or description of substantially identicalconfigurations may be omitted. This is intended to avoid redundancy inthe description below, and to facilitate understanding of those skilledin the art.

It should be noted that the applicant provides the attached drawings andthe following description so that those skilled in the art can fullyunderstand this disclosure. Therefore, the drawings and description arenot intended to limit the subject defined by the claims.

Embodiments 1 to 5

FIGS. 1, 4, 7, 10 and 13 are lens arrangement diagrams of zoom lenssystems according to Embodiments 1 to 5, respectively.

Each of FIGS. 1, 4, 7, 10 and 13 shows a zoom lens system in an infinityin-focus condition. In each Fig., part (a) shows a lens configuration ata wide-angle limit, part (b) shows a lens configuration at a middleposition, and part (c) shows a lens configuration at a telephoto limit.The wide-angle limit is the minimum focal length condition, and thefocal length is expressed by f_(W). The middle position is anintermediate focal length condition, and the focal length is expressedby f_(M)=√(f_(W)*f_(T)). The telephoto limit is the maximum focal lengthcondition, and the focal length is expressed by f_(T). Further, in eachFig., each bent arrow provided between part (a) and part (b) indicates aline obtained by connecting the positions of each lens unit at awide-angle limit, a middle position and a telephoto limit in order fromthe top. Accordingly, in the part between the wide-angle limit and themiddle position, and the part between the middle position and thetelephoto limit, the positions are connected simply with a straightline, and this line does not indicate an actual motion of each lensunit. Furthermore, in each Fig., an arrow imparted to a lens unitindicates focusing from an infinity in-focus condition to a close-objectin-focus condition. That is, in FIGS. 1, 4, 7 and 13, the arrowindicates the direction in which a fourth lens unit G4 described latermoves in focusing from the infinity in-focus condition to theclose-object in-focus condition. In FIG. 10, the arrow indicates thedirection in which a fifth lens unit G5 described later moves infocusing from the infinity in-focus condition to the close-objectin-focus condition.

Each of the zoom lens systems according to Embodiments 1 to 4, in orderfrom the object side to the image side, comprises: a first lens unit G1having positive optical power; a second lens unit G2 having negativeoptical power; a third lens unit G3 having positive optical power; afourth lens unit G4 having negative optical power; and a fifth lens unitG5 having positive optical power. The zoom lens system according toEmbodiment 5, in order from the object side to the image side,comprises: a first lens unit G1 having positive optical power; a secondlens unit G2 having negative optical power; a third lens unit G3 havingpositive optical power; and a fourth lens unit G4 having positiveoptical power.

In the zoom lens systems according to Embodiments 1 to 3, in zooming,the first lens unit G1, the second lens unit G2, the third lens unit G3,and the fourth lens unit G4 move in a direction along the optical axissuch that the intervals between the respective lens units, that is, theinterval between the first lens unit G1 and the second lens unit G2, theinterval between the second lens unit G2 and the third lens unit G3, theinterval between the third lens unit G3 and the fourth lens unit G4, andthe interval between the fourth lens unit G4 and the fifth lens unit G5vary. In the zoom lens system according to Embodiment 4, in zooming, allof the lens units move in the direction along the optical axis such thatthe intervals between the respective lens units, that is, the intervalbetween the first lens unit G1 and the second lens unit G2, the intervalbetween the second lens unit G2 and the third lens unit G3, the intervalbetween the third lens unit G3 and the fourth lens unit G4, and theinterval between the fourth lens unit G4 and the fifth lens unit G5vary. In the zoom lens system according to Embodiment 5, in zooming, allof the lens units move in the direction along the optical axis such thatthe intervals between the respective lens units, that is, the intervalbetween the first lens unit G1 and the second lens unit G2, the intervalbetween the second lens unit G2 and the third lens unit G3, and theinterval between the third lens unit G3 and the fourth lens unit G4vary. In the zoom lens system according to each embodiment, by arrangingthe lens units in a desired optical power configuration, size reductionin the entire lens system is achieved while maintaining high opticalperformance.

In FIGS. 1, 4, 7, 10 and 13, an asterisk “*” imparted to a particularsurface indicates that the surface is aspheric. In each Fig., symbol (+)or (−) imparted to the symbol of each lens unit corresponds to the signof the optical power of the lens unit. In each Fig., the straight linelocated on the most right-hand side indicates the position of the imagesurface S. On the object side relative to the image surface S, i.e.,between the image surface S and the most image side lens surface in thefifth lens unit G5 in FIGS. 1, 4, 7 and 10, or between the image surfaceS and the most image side lens surface in the fourth lens unit G4 inFIG. 13, a plane parallel plate P equivalent to an optical low-passfilter or a face plate of an image sensor is provided.

Embodiment 1

As shown in FIG. 1, the first lens unit G1, in order from the objectside to the image side, comprises: a negative meniscus first lenselement L1 with the convex surface facing the object side; a positivemeniscus second lens element L2 with the convex surface facing theobject side; and a positive meniscus third lens element L3 with theconvex surface facing the object side. Among these, the first lenselement L1 and the second lens element L2 are cemented with each other.In the surface data of the corresponding Numerical Example describedlater, surface number 2 is imparted to an adhesive layer between thefirst lens element L1 and the second lens element L2.

The second lens unit G2, in order from the object side to the imageside, comprises: a negative meniscus fourth lens element L4 with theconvex surface facing the object side; a negative meniscus fifth lenselement L5 with the convex surface facing the image side; and abi-convex sixth lens element L6. Among these, the fourth lens element L4has two aspheric surfaces.

The third lens unit G3, in order from the object side to the image side,comprises: a bi-convex seventh lens element L7; a bi-convex eighth lenselement L8, a bi-concave ninth lens element L9; and a bi-convex tenthlens element L10. Among these, the eighth lens element L8 and the ninthlens element L9 are cemented with each other. In the surface data of thecorresponding Numerical Example described later, surface number 16 isimparted to an adhesive layer between the eighth lens element L8 and theninth lens element L9. The seventh lens element L7 has two asphericsurfaces.

The fourth lens unit G4 comprises solely a negative meniscus eleventhlens element L11 with the convex surface facing the object side.

The fifth lens unit G5 comprises solely a bi-convex twelfth lens elementL12. The twelfth lens element L12 has two aspheric surfaces.

In the zoom lens system according to Embodiment 1, an aperture diaphragmA is provided between the third lens unit G3 and the fourth lens unitG4. In zooming from a wide-angle limit to a telephoto limit at the timeof image taking, the aperture diaphragm A moves along the optical axisto the object side, integrally with the third lens unit G3.

In the zoom lens system according to Embodiment 1, a plane parallelplate P is provided on the object side relative to the image surface S,i.e., between the image surface S and the twelfth lens element L12.

In the zoom lens system according to Embodiment 1, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the fourth lens unit G4 move nearly monotonicallyto the object side, the second lens unit G2 moves to the image side withlocus of a convex to the image side, the third lens unit G3 movesmonotonically to the object side, and the fifth lens unit G5 is fixedwith respect to the image surface S. That is, in zooming, the first lensunit G1, the second lens unit G2, the third lens unit G3, and the fourthlens unit G4 move along the optical axis such that the interval betweenthe first lens unit G1 and the second lens unit G2 increases, theinterval between the second lens unit G2 and the third lens unit G3decreases, the interval between the third lens unit G3 and the fourthlens unit G4 changes, and the interval between the fourth lens unit G4and the fifth lens unit G5 increases.

In the zoom lens system according to Embodiment 1, in focusing from aninfinity in-focus condition to a close-object in-focus condition, thefourth lens unit G4 moves along the optical axis to the image side.

Embodiment 2

As shown in FIG. 4, the first lens unit G1, in order from the objectside to the image side, comprises: a negative meniscus first lenselement L1 with the convex surface facing the object side; a positivemeniscus second lens element L2 with the convex surface facing theobject side; and a positive meniscus third lens element L3 with theconvex surface facing the object side. Among these, the first lenselement L1 and the second lens element L2 are cemented with each other.In the surface data of the corresponding Numerical Example describedlater, surface number 2 is imparted to an adhesive layer between thefirst lens element L1 and the second lens element L2.

The second lens unit G2, in order from the object side to the imageside, comprises: a negative meniscus fourth lens element L4 with theconvex surface facing the object side; a bi-concave fifth lens elementL5; and a bi-convex sixth lens element L6. Among these, the fourth lenselement L4 has two aspheric surfaces.

The third lens unit G3, in order from the object side to the image side,comprises: a bi-convex seventh lens element L7; a positive meniscuseighth lens element L8 with the convex surface facing the object side; anegative meniscus ninth lens element L9 with the convex surface facingthe object side; and a bi-convex tenth lens element L10. Among these,the eighth lens element L8 and the ninth lens element L9 are cementedwith each other. In the surface data of the corresponding NumericalExample described later, surface number 16 is imparted to an adhesivelayer between the eighth lens element L8 and the ninth lens element L9.The seventh lens element L7 has two aspheric surfaces.

The fourth lens unit G4 comprises solely a negative meniscus eleventhlens element L11 with the convex surface facing the object side.

The fifth lens unit G5 comprises solely a bi-convex twelfth lens elementL12. The twelfth lens element L12 has two aspheric surfaces.

In the zoom lens system according to Embodiment 2, an aperture diaphragmA is provided between the third lens unit G3 and the fourth lens unitG4. In zooming from a wide-angle limit to a telephoto limit at the timeof image taking, the aperture diaphragm A moves along the optical axisto the object side, integrally with the third lens unit G3.

In the zoom lens system according to Embodiment 2, a plane parallelplate P is provided on the object side relative to the image surface S,i.e., between the image surface S and the twelfth lens element L12.

In the zoom lens system according to Embodiment 2, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 moves to the object side with locus of a convex tothe image side, the second lens unit G2 moves to the image side withlocus of a convex to the image side, the third lens unit G3 moves nearlymonotonically to the object side, the fourth lens unit G4 movesmonotonically to the object side, and the fifth lens unit G5 is fixedwith respect to the image surface S. That is, in zooming, the first lensunit G1, the second lens unit G2, the third lens unit G3, and the fourthlens unit G4 move along the optical axis such that the interval betweenthe first lens unit G1 and the second lens unit G2 increases, theinterval between the second lens unit G2 and the third lens unit G3decreases, the interval between the third lens unit G3 and the fourthlens unit G4 changes, and the interval between the fourth lens unit G4and the fifth lens unit G5 increases.

In the zoom lens system according to Embodiment 2, in focusing from aninfinity in-focus condition to a close-object in-focus condition, thefourth lens unit G4 moves along the optical axis to the image side.

Embodiment 3

As shown in FIG. 7, the first lens unit G1, in order from the objectside to the image side, comprises: a negative meniscus first lenselement L1 with the convex surface facing the object side; a bi-convexsecond lens element L2; and a positive meniscus third lens element L3with the convex surface facing the object side. Among these, the firstlens element L1 and the second lens element L2 are cemented with eachother. In the surface data of the corresponding Numerical Exampledescribed later, surface number 2 is imparted to an adhesive layerbetween the first lens element L1 and the second lens element L2.

The second lens unit G2, in order from the object side to the imageside, comprises: a negative meniscus fourth lens element L4 with theconvex surface facing the object side; a negative meniscus fifth lenselement L5 with the convex surface facing the image side; and abi-convex sixth lens element L6. Among these, the fourth lens element L4has two aspheric surfaces.

The third lens unit G3, in order from the object side to the image side,comprises: a bi-convex seventh lens element L7; a positive meniscuseighth lens element L8 with the convex surface facing the object side; anegative meniscus ninth lens element L9 with the convex surface facingthe object side; and a bi-convex tenth lens element L10. Among these,the eighth lens element L8 and the ninth lens element L9 are cementedwith each other. In the surface data of the corresponding NumericalExample described later, surface number 16 is imparted to an adhesivelayer between the eighth lens element L8 and the ninth lens element L9.The seventh lens element L7 has two aspheric surfaces.

The fourth lens unit G4 comprises solely a negative meniscus eleventhlens element L11 with the convex surface facing the object side.

The fifth lens unit G5 comprises solely a bi-convex twelfth lens elementL12. The twelfth lens element L12 has two aspheric surfaces.

In the zoom lens system according to Embodiment 3, an aperture diaphragmA is provided between the third lens unit G3 and the fourth lens unitG4. In zooming from a wide-angle limit to a telephoto limit at the timeof image taking, the aperture diaphragm A moves along the optical axisto the object side, integrally with the third lens unit G3.

In the zoom lens system according to Embodiment 3, a plane parallelplate P is provided on the object side relative to the image surface S,i.e., between the image surface S and the twelfth lens element L12.

In the zoom lens system according to Embodiment 3, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 moves nearly monotonically to the object side, thesecond lens unit G2 moves to the image side with locus of a convex tothe image side, the third lens unit G3 moves monotonically to the objectside, the fourth lens unit G4 moves to the object side with locus of aconvex to the image side, and the fifth lens unit G5 is fixed withrespect to the image surface S. That is, in zooming, the first lens unitG1, the second lens unit G2, the third lens unit G3, and the fourth lensunit G4 move along the optical axis such that the interval between thefirst lens unit G1 and the second lens unit G2 increases, the intervalbetween the second lens unit G2 and the third lens unit G3 decreases,the interval between the third lens unit G3 and the fourth lens unit G4changes, and the interval between the fourth lens unit G4 and the fifthlens unit G5 increases.

In the zoom lens system according to Embodiment 3, in focusing from aninfinity in-focus condition to a close-object in-focus condition, thefourth lens unit G4 moves along the optical axis to the image side.

Embodiment 4

As shown in FIG. 10, the first lens unit G1, in order from the objectside to the image side, comprises: a negative meniscus first lenselement L1 with the convex surface facing the object side; a positivemeniscus second lens element L2 with the convex surface facing theobject side; and a positive meniscus third lens element L3 with theconvex surface facing the object side. Among these, the first lenselement L1 and the second lens element L2 are cemented with each other.In the surface data of the corresponding Numerical Example describedlater, surface number 2 is imparted to an adhesive layer between thefirst lens element L1 and the second lens element L2.

The second lens unit G2, in order from the object side to the imageside, comprises: a negative meniscus fourth lens element L4 with theconvex surface facing the object side; a bi-concave fifth lens elementL5; and a bi-convex sixth lens element L6. Among these, the fourth lenselement L4 has two aspheric surfaces, and the fifth lens element L5 hasan aspheric object side surface.

The third lens unit G3, in order from the object side to the image side,comprises: a bi-convex seventh lens element L7; a bi-convex eighth lenselement L8; and a bi-concave ninth lens element L9. Among these, theeighth lens element L8 and the ninth lens element L9 are cemented witheach other. In the surface data of the corresponding Numerical Exampledescribed later, surface number 16 is imparted to an adhesive layerbetween the eighth lens element L8 and the ninth lens element L9. Theseventh lens element L7 has two aspheric surfaces, and the ninth lenselement L9 has an aspheric image side surface.

The fourth lens unit G4 comprises solely a negative meniscus tenth lenselement L10 with the convex surface facing the object side. The tenthlens element L10 has an aspheric object side surface.

The fifth lens unit G5 comprises solely a bi-convex eleventh lenselement L11. The eleventh lens element L11 has two aspheric surfaces.

In the zoom lens system according to Embodiment 4, an aperture diaphragmA is provided between the third lens unit G3 and the fourth lens unitG4. In zooming from a wide-angle limit to a telephoto limit at the timeof image taking, the aperture diaphragm A moves along the optical axisto the object side, integrally with the third lens unit G3.

In the zoom lens system according to Embodiment 4, a plane parallelplate P is provided on the object side relative to the image surface S,i.e., between the image surface S and the eleventh lens element L11.

In the zoom lens system according to Embodiment 4, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move nearly monotonicallyto the object side, the second lens unit G2 and the fifth lens unit G5move nearly monotonically to the image side, and the fourth lens unit G4moves slightly to the object side. That is, in zooming, the first lensunit G1, the second lens unit G2, the third lens unit G3, the fourthlens unit G4, and the fifth lens unit G5 move along the optical axissuch that the interval between the first lens unit G1 and the secondlens unit G2 increases, the interval between the second lens unit G2 andthe third lens unit G3 decreases, the interval between the third lensunit G3 and the fourth lens unit G4 increases, and the interval betweenthe fourth lens unit G4 and the fifth lens unit G5 changes.

In the zoom lens system according to Embodiment 4, in focusing from aninfinity in-focus condition to a close-object in-focus condition, thefifth lens unit G5 moves along the optical axis to the object side.

Embodiment 5

As shown in FIG. 13, the first lens unit G1, in order from the objectside to the image side, comprises: a negative meniscus first lenselement L1 with the convex surface facing the object side; a bi-convexsecond lens element L2; and a positive meniscus third lens element L3with the convex surface facing the object side. Among these, the firstlens element L1 and the second lens element L2 are cemented with eachother. In the surface data of the corresponding Numerical Exampledescribed later, surface number 2 is imparted to an adhesive layerbetween the first lens element L1 and the second lens element L2.

The second lens unit G2, in order from the object side to the imageside, comprises: a negative meniscus fourth lens element L4 with theconvex surface facing the object side; a bi-concave fifth lens elementL5; and a positive meniscus sixth lens element L6 with the convexsurface facing the object side.

The third lens unit G3, in order from the object side to the image side,comprises: a bi-convex seventh lens element L7; a bi-convex eighth lenselement L8; and a bi-concave ninth lens element L9. Among these, theeighth lens element L8 and the ninth lens element L9 are cemented witheach other. In the surface data of the corresponding Numerical Exampledescribed later, surface number 16 is imparted to an adhesive layerbetween the eighth lens element L8 and the ninth lens element L9. Theeighth lens element L8 has an aspheric object side surface.

The fourth lens unit G4 comprises solely a positive meniscus tenth lenselement L10 with the convex surface facing the object side. The tenthlens element L10 has two aspheric surfaces.

In the zoom lens system according to Embodiment 5, an aperture diaphragmA is provided between the third lens unit G3 and the fourth lens unitG4. In zooming from a wide-angle limit to a telephoto limit at the timeof image taking, the aperture diaphragm A moves along the optical axisto the object side, integrally with the third lens unit G3.

In the zoom lens system according to Embodiment 5, a plane parallelplate P is provided on the object side relative to the image surface S,i.e., between the image surface S and the tenth lens element L10.

In the zoom lens system according to Embodiment 5, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move nearly monotonicallyto the object side, the second lens unit G2 moves nearly monotonicallyto the image side, and the fourth lens unit G4 moves to the image sidewith locus of a convex to the object side. That is, in zooming, thefirst lens unit G1, the second lens unit G2, the third lens unit G3, andthe fourth lens unit G4 move along the optical axis such that theinterval between the first lens unit G1 and the second lens unit G2increases, the interval between the second lens unit G2 and the thirdlens unit G3 decreases, and the interval between the third lens unit G3and the fourth lens unit G4 changes.

In the zoom lens system according to Embodiment 5, in focusing from aninfinity in-focus condition to a close-object in-focus condition, thefourth lens unit G4 moves along the optical axis to the object side.

In the zoom lens systems according to Embodiments 1 to 5, the aperturediaphragm A is provided between the third lens unit G3 and the fourthlens unit G4. In zooming from a wide-angle limit to a telephoto limit atthe time of image taking, the aperture diaphragm A moves along theoptical axis, integrally with the third lens unit G3. Therefore, it ispossible to reduce the size of the entire lens system while maintaininghigh optical performance.

In the zoom lens systems according to Embodiments 1 to 5, the third lensunit G3 includes two or more lens elements, and one or moreinter-lens-element air spaces. Therefore, it is possible to successfullycompensate aberrations, and it is possible to reduce the size of theentire lens system while maintaining high optical performance and havinga high zooming ratio.

In the zoom lens systems according to Embodiments 1 to 5, since thefourth lens unit G4 is composed of one lens element, reduction in thesize of the entire lens system is achieved. Further, in the zoom lenssystems according to Embodiments 1 to 3 and 5, rapid focusing from aninfinity in-focus condition to a close-object in-focus condition iseasily achieved.

In the zoom lens systems according to Embodiments 1 to 4, since thefifth lens unit G5 is composed of one lens element, reduction in thesize of the entire lens system is achieved. Further, in the zoom lenssystem according to Embodiment 4, rapid focusing from an infinityin-focus condition to a close-object in-focus condition is easilyachieved.

In the zoom lens systems according to Embodiments 1 to 5, in focusingfrom an infinity in-focus condition to a close-object in-focuscondition, the fourth lens unit G4 or the fifth lens unit G5 moves alongthe optical axis. Therefore, high optical performance can be maintainedeven in the close-object in-focus condition.

The zoom lens systems according to Embodiments 1 to 4 each have afive-unit configuration, and the zoom lens system according toEmbodiment 5 has a four-unit configuration. However, the number of lensunits constituting each lens system is not particularly limited as longas it is not less than four. Further, the optical powers of the fourthlens unit G4 and the lens units located on the image side relative tothe fourth lens unit G4 are not particularly limited.

Any lens unit among the first to fifth lens units G1 to G5 or a sub lensunit corresponding to a part of each lens unit in the zoom lens systemsaccording to Embodiments 1 to 4, or any lens units among the first tofourth lens units G1 to G4 or a sub lens unit corresponding to a part ofeach lens unit in the zoom lens system according to Embodiment 5, may bemoved in a direction perpendicular to the optical axis. Thereby,movement of an image point caused by vibration of the entire system canbe compensated, that is, image blur caused by hand blurring, vibrationand the like can be optically compensated.

When compensating the movement of the image point caused by vibration ofthe entire system, for example, the third lens unit G3 may be moved inthe direction perpendicular to the optical axis. Thereby, image blur canbe compensated in a state that size increase in the entire zoom lenssystem is suppressed to realize a compact configuration and thatexcellent imaging characteristics such as small decentering comaaberration and small decentering astigmatism are satisfied.

In a case where a lens unit is composed of a plurality of lens elements,the above-mentioned sub lens unit corresponding to a part of each lensunit indicates any one lens element or a plurality of adjacent lenselements among the plurality of lens elements.

As described above, Embodiments 1 to 5 have been described as examplesof art disclosed in the present application. However, the art in thepresent disclosure is not limited to these embodiments. It is understoodthat various modifications, replacements, additions, omissions, and thelike have been performed in these embodiments to give optionalembodiments, and the art in the present disclosure can be applied to theoptional embodiments.

The following description is given for conditions to be satisfied by azoom lens system like the zoom lens systems according to Embodiments 1to 5. Here, a plurality of beneficial conditions is set forth for thezoom lens system according to each embodiment. A construction thatsatisfies all the plural conditions is most beneficial for the zoom lenssystem. However, when an individual condition is satisfied, a zoom lenssystem having the corresponding effect is obtained.

For example, in a zoom lens system, like the zoom lens systems accordingto Embodiments 1 to 5, which, in order from the object side to the imageside, comprises: a first lens unit having positive optical power; asecond lens unit having negative optical power; a third lens unit havingpositive optical power; a fourth lens unit having optical power; and anaperture diaphragm provided between the third lens unit and the fourthlens unit, wherein, in zooming from a wide-angle limit to a telephotolimit at the time of image taking, the first lens unit, the second lensunit, and the third lens unit are moved along an optical axis to performmagnification change, and the third lens unit includes two or more lenselements, and one or more inter-lens-element air spaces, the followingconditions (1) and (a) are satisfied. Hereinafter, the lensconfiguration of this zoom lens system is referred to as a basicconfiguration of the embodiment.−7.0<f ₁ /f ₂<−4.0  (1)f _(T) /f _(W)>9.0  (a)

where,

f₁ is a composite focal length of the first lens unit,

f₂ is a composite focal length of the second lens unit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

f_(T) is a focal length of the entire system at a telephoto limit.

The condition (a) sets forth the ratio between the focal length of theentire system at a wide-angle limit and the focal length of the entiresystem at a telephoto limit. The zoom lens system having the basicconfiguration satisfies the condition (a), and therefore, has a highzooming ratio, and ensures high magnification.

The condition (1) sets forth the ratio between the focal length of thefirst lens unit and the focal length of the second lens unit. When thevalue goes below the lower limit of the condition (1), the focal lengthof the second lens unit becomes excessively short, and aberrationfluctuation at the time of magnification change increases, which causesdifficulty in compensating aberrations. Further, the focal length of thefirst lens unit becomes excessively long, and the amount of movement ofthe first lens unit, which is desired for securing high magnification,becomes excessively great, which causes difficulty in providing compactlens barrels, imaging devices, and cameras. When the value exceeds theupper limit of the condition (1), the focal length of the first lensunit becomes excessively short, and aberration fluctuation at the timeof magnification change increases, which causes difficulty incompensating aberrations. In addition, the diameter of the first lensunit increases, which causes difficulty in providing compact lensbarrels, imaging devices, and cameras. Further, error sensitivity toinclination of the first lens unit becomes excessively high, which maycause difficulty in assembling optical systems.

It is beneficial that the condition (1) is satisfied under the followingcondition (a)′.f _(T) /f _(W)>13.0  (a)′

For example, in a zoom lens system having the basic configuration likethe zoom lens systems according to Embodiments 1 to 5, it is beneficialthat the following condition (2) is satisfied.0.5<|f ₁ /f ₄|<4.2  (2)

where,

f₁ is a composite focal length of the first lens unit, and

f₄ is a composite focal length of the fourth lens unit.

The condition (2) sets forth the ratio between the focal length of thefirst lens unit and the focal length of the fourth lens unit. When thevalue goes below the lower limit of the condition (2), the focal lengthof the fourth lens unit becomes excessively long, and the amount ofmovement of the fourth lens unit becomes excessively great, which causesdifficulty in providing compact lens barrels, imaging devices, andcameras. Further, the focal length of the first lens unit becomesexcessively short, and aberration fluctuation at the time ofmagnification change increases, which causes difficulty in compensatingaberrations. In addition, the diameter of the first lens unit increases,which causes difficulty in providing compact lens barrels, imagingdevices, and cameras. Further, error sensitivity to inclination of thefirst lens unit becomes excessively high, which may cause difficulty inassembling optical systems. When the value exceeds the upper limit ofthe condition (2), the focal length of the first lens unit becomesexcessively long, and the amount of movement of the first lens unit,which is desired for securing high magnification, becomes excessivelygreat, which causes difficulty in providing compact lens barrels,imaging devices, and cameras.

When at least one of the following conditions (2)′ and (2)″ issatisfied, the above-mentioned effect is achieved more successfully.1.5<|f ₁ /f ₄|  (2)′|f ₁ /f ₄|<3.0  (2)″

It is beneficial that the conditions (2), (2)′, and (2)″ are satisfiedunder the above condition (a)′.

For example, in a zoom lens system having the basic configuration likethe zoom lens systems according to Embodiments 1 to 5, it is beneficialthat the following condition (3) is satisfied.0.8<L _(T) /f _(T)<1.4  (3)

where,

L_(T) is an overall length of lens system (a distance from a most objectside surface of the first lens unit to an image surface) at a telephotolimit, and

f_(T) is a focal length of the entire system at a telephoto limit.

The condition (3) sets forth the ratio between the overall length oflens system at a telephoto limit and the focal length of the entiresystem at a telephoto limit. When the value goes below the lower limitof the condition (3), the overall length of lens system at a telephotolimit becomes excessively short, and the focal length of each lens unitbecomes excessively short. Thereby, aberration fluctuation at the timeof magnification change increases, which causes difficulty incompensating aberrations. When the value exceeds the upper limit of thecondition (3), the overall length of lens system at a telephoto limitbecomes excessively long, which causes difficulty in providing compactlens barrels, imaging devices, and cameras.

When at least one of the following conditions (3)′ and (3)″ issatisfied, the above-mentioned effect is achieved more successfully.0.9<L _(T) /f _(T)  (3)′L _(T) /f _(T)<1.2  (3)″

It is beneficial that the conditions (3), (3)′, and (3)″ are satisfiedunder the above condition (a)′.

Each of the lens units constituting the zoom lens systems according toEmbodiments 1 to 5 is composed exclusively of refractive type lenselements that deflect the incident light by refraction, i.e., lenselements of a type in which deflection is achieved at the interfacebetween media each having a distinct refractive index. However, thepresent disclosure is not limited to this. For example, the lens unitsmay employ diffractive type lens elements that deflect the incidentlight by diffraction; refractive-diffractive hybrid type lens elementsthat deflect the incident light by a combination of diffraction andrefraction; or gradient index type lens elements that deflect theincident light by distribution of refractive index in the medium. Inparticular, in the refractive-diffractive hybrid type lens elements,when a diffraction structure is formed in the interface between mediahaving mutually different refractive indices, wavelength dependence inthe diffraction efficiency is improved. Thus, such a configuration isbeneficial.

Moreover, in each embodiment, a configuration has been described that onthe object side relative to the image surface S, i.e., between the imagesurface S and the most image side lens surface of the fifth lens unit G5in Embodiments 1 to 4, or between the image surface S and the most imageside lens surface of the fourth lens unit G4 in Embodiment 5, a planeparallel plate P such as an optical low-pass filter and a face plate ofan image sensor is provided. This low-pass filter may be: a birefringenttype low-pass filter made of, for example, a crystal whose predeterminedcrystal orientation is adjusted; or a phase type low-pass filter thatachieves desired characteristics of optical cut-off frequency bydiffraction.

Embodiment 6

FIG. 16 is a schematic configuration diagram of a digital still cameraaccording to Embodiment 6. In FIG. 16, the digital still cameracomprises: an imaging device having a zoom lens system 1 and an imagesensor 2 that is a CCD; a liquid crystal display monitor 3; and a body4. A zoom lens system according to Embodiment 1 is employed as the zoomlens system 1. In FIG. 16, the zoom lens system 1 comprises a first lensunit G1, a second lens unit G2, a third lens unit G3, an aperturediaphragm A, a fourth lens unit G4, and a fifth lens unit G5. In thebody 4, the zoom lens system 1 is arranged on the front side, and theimage sensor 2 is arranged on the rear side of the zoom lens system 1.On the rear side of the body 4, the liquid crystal display monitor 3 isarranged, and an optical image of a photographic object generated by thezoom lens system 1 is formed on an image surface S.

A lens barrel comprises a main barrel 5, a moving barrel 6, and acylindrical cam 7. When the cylindrical cam 7 is rotated, the first lensunit G1, the second lens unit G2, the third lens unit G3 and theaperture diaphragm A, the fourth lens unit G4, and the fifth lens unitG5 move to predetermined positions relative to the image sensor 2, sothat zooming from a wide-angle limit to a telephoto limit is achieved.The fourth lens unit G4 is movable in the optical axis direction by amotor for focus adjustment.

As such, when the zoom lens system according to Embodiment 1 is employedin a digital still camera, a small digital still camera can be obtainedthat has a high resolution and high capability of compensating curvatureof field and that has a short overall length of lens system at the timeof non-use. In the digital still camera shown in FIG. 16, any one of thezoom lens systems according to Embodiments 2 to 5 may be employed inplace of the zoom lens system according to Embodiment 1. Further, theoptical system of the digital still camera shown in FIG. 16 isapplicable also to a digital video camera for moving images. In thiscase, moving images with high resolution can be acquired in addition tostill images.

The digital still camera according to Embodiment 6 has been describedfor a case that the employed zoom lens system 1 is any one of the zoomlens systems according to Embodiments 1 to 5. However, in these zoomlens systems, the entire zooming range need not be used. That is, inaccordance with a desired zooming range, a range where satisfactoryoptical performance is obtained may exclusively be used. Then, the zoomlens system may be used as one having a lower magnification than thezoom lens system described in Embodiments 1 to 5.

Further, Embodiment 6 has been described for a case that the zoom lenssystem is applied to a lens barrel of so-called barrel retractionconstruction. However, the present invention is not limited to this. Forexample, the zoom lens system may be applied to a lens barrel ofso-called bending configuration where a prism having an internalreflective surface or a front surface reflective mirror is arranged atan arbitrary position within the first lens unit G1 or the like.Further, in Embodiment 6, the zoom lens system may be applied to aso-called sliding lens barrel in which a part of the lens unitsconstituting the zoom lens system like the entirety of the second lensunit G2, the entirety of the third lens unit G3, or alternatively a partof the second lens unit G2 or the third lens unit G3 is caused to escapefrom the optical axis at the time of barrel retraction.

An imaging device comprising any one of the zoom lens systems accordingto Embodiments 1 to 5, and an image sensor such as a CCD or a CMOS maybe applied to a mobile terminal device such as a smart-phone, a PersonalDigital Assistance, a surveillance camera in a surveillance system, aWeb camera, a vehicle-mounted camera or the like.

As described above, Embodiment 6 has been described as an example of artdisclosed in the present application. However, the art in the presentdisclosure is not limited to this embodiment. It is understood thatvarious modifications, replacements, additions, omissions, and the likehave been performed in this embodiment to give optional embodiments, andthe art in the present disclosure can be applied to the optionalembodiments.

Numerical examples are described below in which the zoom lens systemsaccording to Embodiments 1 to 5 are implemented. In the numericalexamples, the units of the length in the tables are all “mm”, while theunits of the view angle in the tables are all “°”. In the numericalexamples, r is the radius of curvature, d is the axial distance, nd isthe refractive index to the d-line, and vd is the Abbe number to thed-line. In the numerical examples, the surfaces marked with * areaspheric surfaces, and the aspheric surface configuration is defined bythe following expression.

$Z = {\frac{h^{2}/r}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h/r} \right)^{2}}}} + {A\; 4h^{4}} + {A\; 6h^{6}} + {A\; 8h^{8}} + {A\; 10h^{10}} + {A\; 12h^{12}} + {A\; 14h^{14}}}$Here, κ is the conic constant, A4, A6, A8, A10, A12 and A14 are afourth-order, sixth-order, eighth-order, tenth-order, twelfth-order andfourteenth-order aspherical coefficients, respectively.

FIGS. 2, 5, 8, 11 and 14 are longitudinal aberration diagrams of thezoom lens systems according to Numerical Examples 1 to 5, respectively.

In each longitudinal aberration diagram, part (a) shows the aberrationat a wide-angle limit, part (b) shows the aberration at a middleposition, and part (c) shows the aberration at a telephoto limit. Eachlongitudinal aberration diagram, in order from the left-hand side, showsthe spherical aberration, the astigmatism and the distortion. In eachFig., the spherical aberration is indicated as “SA(mm)”, the astigmatismis indicated as “AST(mm)”, and the distortion is indicated as “DIS(%)”.In each spherical aberration diagram, the vertical axis indicates theF-number, and the solid line, the short dash line and the long dash lineindicate the characteristics to the d-line having a wavelength of 587.56nm, the F-line having a wavelength of 486.13 nm and the C-line having awavelength of 656.28 nm, respectively. In each astigmatism diagram, thevertical axis indicates the image height, and the solid line and thedash line indicate the characteristics to the sagittal plane and themeridional plane, respectively. In each distortion diagram, the verticalaxis indicates the image height. In each Fig., the F-number is indicatedas “F”, the image height is indicated as “H”, the sagittal plane isindicated as “s”, and the meridional plane is indicated as “m”.

FIGS. 3, 6, 9, 12 and 15 are lateral aberration diagrams of the zoomlens systems at a telephoto limit according to Numerical Examples 1 to5, respectively.

In each lateral aberration diagram, the aberration diagrams in the upperthree parts correspond to a basic state where image blur compensation isnot performed at a telephoto limit, while the aberration diagrams in thelower three parts correspond to an image blur compensation state wherethe entirety of the third lens unit G3 is moved by a predeterminedamount in a direction perpendicular to the optical axis at a telephotolimit. Among the lateral aberration diagrams of a basic state, the upperpart shows the lateral aberration at an image point of 70% of themaximum image height, the middle part shows the lateral aberration atthe axial image point, and the lower part shows the lateral aberrationat an image point of −70% of the maximum image height. Among the lateralaberration diagrams of an image blur compensation state, the upper partshows the lateral aberration at an image point of 70% of the maximumimage height, the middle part shows the lateral aberration at the axialimage point, and the lower part shows the lateral aberration at an imagepoint of −70% of the maximum image height. In each lateral aberrationdiagram, the horizontal axis indicates the distance from the principalray on the pupil surface, and the solid line, the short dash line andthe long dash line indicate the characteristics to the d-line, theF-line and the C-line, respectively. In each lateral aberration diagram,the meridional plane is adopted as the plane containing the optical axisof the first lens unit G1 and the optical axis of the third lens unitG3.

In the zoom lens system according to each of the numerical examples, theamount of movement of the third lens unit G3 in a directionperpendicular to the optical axis in an image blur compensation state ata telephoto limit is as follows.

Numerical Example 1 0.094 mm

Numerical Example 2 0.082 mm

Numerical Example 3 0.105 mm

Numerical Example 4 0.125 mm

Numerical Example 5 0.197 mm

Here, when the shooting distance is infinity, at a telephoto limit, theamount of image decentering in a case that the zoom lens system inclinesby 0.3° is equal to the amount of image decentering in a case that theentirety of the third lens unit G3 moves in parallel by each of theabove-mentioned values in a direction perpendicular to the optical axis.

As seen from the lateral aberration diagrams, satisfactory symmetry isobtained in the lateral aberration at the axial image point. Further,when the lateral aberration at the +70% image point and the lateralaberration at the −70% image point are compared with each other in abasic state, all have a small degree of curvature and almost the sameinclination in the aberration curve. Thus, decentering coma aberrationand decentering astigmatism are small. This indicates that sufficientimaging performance is obtained even in an image blur compensationstate. Further, when the image blur compensation angle of a zoom lenssystem is the same, the amount of parallel movement desired for imageblur compensation decreases with decreasing focal length of the entirezoom lens system. Thus, at arbitrary zoom positions, sufficient imageblur compensation can be performed for image blur compensation angles upto 0.3° without degrading the imaging characteristics.

Numerical Example 1

The zoom lens system of Numerical Example 1 corresponds to Embodiment 1shown in FIG. 1. Table 1 shows the surface data of the zoom lens systemof Numerical Example 1. Table 2 shows the aspherical data. Table 3 showsvarious data.

TABLE 1 (Surface data) Surface number r d nd vd Object surface ∞  139.12230 0.75000 1.84666 23.8  2 24.34130 0.01000 1.56732 42.8  324.34130 2.57250 1.49700 81.6  4 669.01800 0.15000  5 24.12950 1.796801.72916 54.7  6 79.16250 Variable  7* 40.41520 0.50000 1.87702 37.0  8*4.92640 3.70580  9 −8.33810 0.30000 1.72916 54.7 10 −88.01810 0.22870 1127.63010 1.21460 1.94595 18.0 12 −34.07630 Variable 13* 5.61650 2.154501.58332 59.1 14* −22.78570 0.50340 15 8.07340 1.26250 1.49700 81.6 16−490.35460 0.01000 1.56732 42.8 17 −490.35460 0.30000 1.90366 31.3 184.81270 0.35810 19 12.15960 1.20290 1.52996 55.8 20 −11.64830 0.4000021(Diaphragm) ∞ Variable 22 30.16120 0.50000 1.88300 40.8 23 8.20900Variable 24* 9.68560 2.23030 1.52996 55.8 25* −93.78700 2.36430 26 ∞0.78000 1.51680 64.2 27 ∞ (BF) Image surface ∞

TABLE 2 (Aspherical data) Surface No. 7 K = 0.00000E+00, A4 =−5.63481E−04, A6 = 3.11555E−05, A8 = −8.17750E−07 A10 = 8.06105E−09, A12= 0.00000E+00 Surface No. 8 K = 0.00000E+00, A4 = −8.76674E−04, A6 =−1.12420E−05, A8 = 2.70324E−06 A10 = −1.33807E−07, A12 = 0.00000E+00Surface No. 13 K = 0.00000E+00, A4 = −7.29201E−04, A6 = −1.17969E−05, A8= −6.10823E−06 A10 = 6.74583E−07, A12 = −4.48240E−08 Surface No. 14 K =0.00000E+00, A4 = 8.59168E−05, A6 = −2.47587E−05, A8 = −1.87567E−06 A10= 1.46231E−07, A12 = −2.05601E−08 Surface No. 24 K = 0.00000E+00, A4 =−6.47588E−04, A6 = 8.67198E−05, A8 = −5.62682E−06 A10 = 1.93110E−07, A12= −4.72323E−09 Surface No. 25 K = 0.00000E+00, A4 = −7.33472E−04, A6 =3.89493E−05, A8 = −1.04425E−06 A10 = −4.32516E−08, A12 = 0.00000E+00

TABLE 3 (Various data) Zooming ratio 14.71263 Wide-angle MiddleTelephoto limit position limit Focal length 4.4482 17.0693 65.4446F-number 3.44055 4.49104 6.16167 View angle 45.0718 12.6331 3.4043 Imageheight 3.7000 3.9000 3.9000 Overall length 46.3632 51.3938 62.4654 oflens system BF 0.48241 0.50874 0.45483 d6 0.3000 10.7372 21.3604 d1216.7953 5.1183 0.3000 d21 3.4276 9.1186 10.4391 d23 2.0635 2.6166 6.6167Entrance pupil 11.0268 35.9621 125.0203 position Exit pupil −11.4186−20.0329 −54.5925 position Front principal 13.8124 38.8475 112.6593points position Back principal 41.9150 34.3246 −2.9791 points positionSingle lens data Lens Initial surface element number Focal length 1 1−77.9069 2 3 50.7587 3 5 46.9551 4 7 −6.4393 5 9 −12.6519 6 11 16.2860 713 7.9466 8 15 15.9947 9 17 −5.2725 10 19 11.4258 11 22 −12.9111 12 2416.6900 Zoom lens unit data Initial Overall Lens surface Focal length ofFront principal Back principal unit No. length lens unit points positionpoints position 1 1 36.28987 5.27930 1.15149 3.09442 2 7 −5.851945.94910 0.35671 1.13559 3 13 9.23453 6.19140 −0.30820 1.47404 4 22−12.91111 0.50000 0.36877 0.60037 5 24 16.68996 5.37460 0.13748 1.16482Magnification of zoom lens unit Lens Initial Wide-angle Middle Telephotounit surface No. limit position limit 1 1 0.00000 0.00000 0.00000 2 7−0.21205 −0.34104 −0.89535 3 13 −0.48200 −1.12114 −1.38610 4 22 1.668251.71504 2.01678 5 24 0.71886 0.71728 0.72051

Numerical Example 2

The zoom lens system of Numerical Example 2 corresponds to Embodiment 2shown in FIG. 4. Table 4 shows the surface data of the zoom lens systemof Numerical Example 2. Table 5 shows the aspherical data. Table 6 showsvarious data.

TABLE 4 (Surface data) Surface number r d nd vd Object surface ∞  131.08320 0.75000 1.84666 23.8  2 20.54660 0.01000 1.56732 42.8  320.54660 2.64550 1.49700 81.6  4 152.85880 0.15000  5 24.63830 1.662801.72916 54.7  6 107.30480 Variable  7* 49.15490 0.50000 1.87702 37.0  8*5.54240 3.71900  9 −10.64890 0.30000 1.72916 54.7 10 112.56090 0.2246011 20.71430 1.29040 1.94595 18.0 12 −81.81860 Variable 13* 5.436801.87130 1.58332 59.1 14* −22.36220 0.40260 15 6.57880 1.45360 1.4970081.6 16 46.91020 0.01000 1.56732 42.8 17 46.91020 0.30000 1.90366 31.318 4.17360 0.30410 19 7.92300 1.07350 1.52996 55.8 20 −15.71980 0.4000021(Diaphragm) ∞ Variable 22 19.40140 0.50000 1.88300 40.8 23 5.56050Variable 24* 9.90500 2.27410 1.52996 55.8 25* −84.49410 2.25770 26 ∞0.78000 1.51680 64.2 27 ∞ (BF) Image surface ∞

TABLE 5 (Aspherical data) Surface No. 7 K = 0.00000E+00, A4 =−6.82260E−04, A6 = 3.42662E−05, A8 = −7.06863E−07 A10 = 5.24073E−09, A12= 0.00000E+00 Surface No. 8 K = 0.00000E+00, A4 = −8.55257E−04, A6 =−2.08462E−06, A8 = 2.57595E−06 A10 = −7.86710E−08, A12 = 0.00000E+00Surface No. 13 K = 0.00000E+00, A4 = −7.38915E−04, A6 = 6.12372E−06, A8= −7.45037E−06 A10 = 7.92758E−07, A12 = −5.22500E−08 Surface No. 14 K =0.00000E+00, A4 = 1.71678E−04, A6 = 7.80329E−06, A8 = −4.99088E−06 A10 =3.22395E−07, A12 = −2.42946E−08 Surface No. 24 K = 0.00000E+00, A4 =−4.14254E−04, A6 = 1.04417E−04, A8 = −5.96937E−06 A10 = 1.47200E−07, A12= −3.27839E−09 Surface No. 25 K = 0.00000E+00, A4 = −8.50740E−04, A6 =9.56957E−05, A8 = −5.15879E−06 A10 = 3.50417E−08, A12 = 0.00000E+00

TABLE 6 (Various data) Zooming ratio 11.03063 Wide-angle MiddleTelephoto limit position limit Focal length 4.4498 14.8500 49.0837F-number 3.44101 4.73422 6.16062 View angle 42.8989 14.5685 4.5571 Imageheight 3.5000 3.9000 3.9000 Overall length 47.2343 46.2180 52.9687 oflens system BF 0.48722 0.48685 0.45643 d6 0.3000 8.1432 17.4571 d1219.1524 6.1570 0.3000 d21 1.6677 4.6342 6.6017 d23 2.7478 3.9176 5.2743Entrance pupil 12.0384 30.0889 89.9355 position Exit pupil −10.1822−16.6238 −24.5944 position Front principal 14.6324 32.0509 42.8463points position Back principal 42.7846 31.3680 3.8850 points positionSingle lens data Lens Initial surface element number Focal length 1 1−74.0055 2 3 47.4464 3 5 43.4920 4 7 −7.1611 5 9 −13.3284 6 11 17.5816 713 7.6883 8 15 15.2143 9 17 −5.0866 10 19 10.0990 11 22 −8.9793 12 2416.8698 Zoom lens unit data Initial Overall Lens surface Focal length ofFront principal Back principal unit No. length lens unit points positionpoints position 1 1 33.79578 5.21830 1.12238 3.01496 2 7 −6.261396.03400 0.48676 1.44491 3 13 8.11525 5.81510 −0.43186 1.41460 4 22−8.97929 0.50000 0.37862 0.60851 5 24 16.86977 5.31180 0.15727 1.19825Magnification of zoom lens unit Lens Initial Wide-angle Middle Telephotounit surface No. limit position limit 1 1 0.00000 0.00000 0.00000 2 7−0.25511 −0.37491 −0.84760 3 13 −0.35202 −0.75087 −1.02588 4 22 2.015962.14616 2.29086 5 24 0.72728 0.72730 0.72910

Numerical Example 3

The zoom lens system of Numerical Example 3 corresponds to Embodiment 3shown in FIG. 7. Table 7 shows the surface data of the zoom lens systemof Numerical Example 3. Table 8 shows the aspherical data. Table 9 showsvarious data.

TABLE 7 (Surface data) Surface number r d nd vd Object surface ∞  157.54400 0.75000 1.84666 23.8  2 32.90100 0.01000 1.56732 42.8  332.90100 2.61090 1.49700 81.6  4 −118.20340 0.15000  5 24.21850 1.525901.72916 54.7  6 50.97680 Variable  7* 29.35900 0.50000 1.87702 37.0  8*5.29960 4.05300  9 −7.89080 0.30000 1.72916 54.7 10 −60.13670 0.23680 1141.52720 1.27550 1.94595 18.0 12 −26.55800 Variable 13* 6.06960 2.371101.58332 59.1 14* −23.88150 0.31890 15 7.14320 1.38840 1.49700 81.6 16109.61190 0.01000 1.56732 42.8 17 109.61190 0.30000 1.90366 31.3 184.95430 0.45800 19 23.14400 1.09800 1.52996 55.8 20 −12.30130 0.4000021(Diaphragm) ∞ Variable 22 30.20470 0.50000 1.88300 40.8 23 10.26950Variable 24* 10.66430 2.04270 1.52996 55.8 25* −98.22820 2.84340 26 ∞0.78000 1.51680 64.2 27 ∞ (BF) Image surface ∞

TABLE 8 Aspherical data) Surface No. 7 K = 0.00000E+00, A4 =−7.15790E−04, A6 = 3.34579E−05, A8 = −6.64896E−07 A10 = 4.88846E−09, A12= 0.00000E+00 Surface No. 8 K = 0.00000E+00, A4 = −9.90606E−04, A6 =−3.67284E−06, A8 = 1.95498E−06 A10 = −6.58573E−08, A12 = 0.00000E+00Surface No. 13 K = 0.00000E+00, A4 = −6.16082E−04, A6 = −3.68104E−07, A8= −5.75983E−06 A10 = 5.43157E−07, A12 = −2.72234E−08 Surface No. 14 K =0.00000E+00, A4 = 1.78340E−05, A6 = −3.72044E−06, A8 = −4.60879E−06 A10= 4.06332E−07, A12 = −2.11784E−08 Surface No. 24 K = 0.00000E+00, A4 =−1.08567E−03, A6 = 1.14745E−04, A8 = −6.05001E−06 A10 = 1.55891E−07, A12= −2.89195E−09 Surface No. 25 K = 0.00000E+00, A4 = −1.36541E−03, A6 =1.09701E−04, A8 = −4.19438E−06 A10 = 2.41875E−08, A12 = 0.00000E+00

TABLE 9 (Various data) Zooming ratio 16.47230 Wide-angle MiddleTelephoto limit position limit Focal length 4.4501 18.0934 73.3027F-number 3.44164 4.20219 6.16157 View angle 41.5033 11.9452 3.0330 Imageheight 3.4000 3.9000 3.9000 Overall length 49.0167 55.3864 70.1058 oflens system BF 0.49135 0.52241 0.45938 d6 0.3000 12.2557 24.4860 d1218.5099 5.2649 0.3000 d21 3.6190 11.3314 12.4827 d23 2.1738 2.08948.4551 Entrance pupil 11.3371 38.4866 134.4812 position Exit pupil−12.3397 −22.9441 −128.8978 position Front principal 14.2438 42.6294166.2455 points position Back principal 44.5666 37.2930 −3.1969 pointsposition Single lens data Lens Initial surface element number Focallength 1 1 −92.0253 2 3 52.0843 3 5 61.7901 4 7 −7.4461 5 9 −12.4864 611 17.2815 7 13 8.5459 8 15 15.3058 9 17 −5.7498 10 19 15.3205 11 22−17.8312 12 24 18.2708 Zoom lens unit data Initial Overall Lens surfaceFocal length of Front principal Back principal unit No. length lens unitpoints position points position 1 1 41.06452 5.04680 1.21748 3.07560 2 7−6.41603 6.36530 0.48274 1.30249 3 13 10.09615 6.34440 −0.66695 1.360634 22 −17.83121 0.50000 0.40711 0.63842 5 24 18.27085 5.66610 0.131611.09620 Magnification of zoom lens unit Lens Initial Wide-angle MiddleTelephoto unit surface No. limit position limit 1 1 0.00000 0.000000.00000 2 7 −0.20116 −0.32179 −0.83233 3 13 −0.49210 −1.25492 −1.58845 422 1.51412 1.51273 1.86297 5 24 0.72299 0.72129 0.72474

Numerical Example 4

The zoom lens system of Numerical Example 4 corresponds to Embodiment 4shown in FIG. 10. Table 10 shows the surface data of the zoom lenssystem of Numerical Example 4. Table 11 shows the aspherical data. Table12 shows various data.

TABLE 10 (Surface data) Surface number r d nd vd Object surface ∞  134.34930 0.65000 1.84666 23.8  2 21.47750 0.01000 1.56732 42.8  321.47750 2.03800 1.49700 81.6  4 147.07180 0.15000  5 26.49040 1.618601.77250 49.6  6 130.70190 Variable  7* 57.01000 0.30000 1.84973 40.6  8*5.45040 3.07830  9* −17.37380 0.40000 1.77200 50.0 10 41.76440 0.1501011 15.48890 1.19800 1.94595 18.0 12 −395.30340 Variable 13* 5.072601.87320 1.51776 69.9 14* −14.52160 0.29090 15 7.30900 1.14640 1.6968055.5 16 −66.82490 0.01000 1.56732 42.8 17 −66.82490 0.30000 1.68400 31.318* 3.87590 0.50000 19(Diaphragm) ∞ Variable 20* 12.63810 0.500001.68400 31.3 21 8.93930 Variable 22* 26.96660 1.68640 1.58332 59.1 23*−17.12980 Variable 24 ∞ 0.78000 1.51680 64.2 25 ∞ (BF) Image surface ∞

TABLE 11 (Aspherical data) Surface No. 7 K = 0.00000E+00, A4 =−8.94401E−04, A6 = 6.21567E−05, A8 = −1.98151E−06 A10 = 2.99161E−08, A12= −1.77821E−10, A14 = 0.00000E+00 Surface No. 8 K = 0.00000E+00, A4 =−1.06030E−03, A6 = 2.36965E−05, A8 = 1.64213E−06 A10 = −5.56501E−08, A12= −1.14121E−09, A14 = 0.00000E+00 Surface No. 9 K = 0.00000E+00, A4 =5.29698E−05, A6 = −3.68820E−06, A8 = 3.32156E−07 A10 = −6.16745E−09, A12= 0.00000E+00, A14 = 0.00000E+00 Surface No. 13 K = 0.00000E+00, A4 =−7.42045E−04, A6 = −9.81495E−06, A8 = −1.14627E−05 A10 = 2.41648E−06,A12 = −2.74102E−07, A14 = 1.22994E−08 Surface No. 14 K = 0.00000E+00, A4= 6.07823E−04, A6 = −6.47865E−05, A8 = 4.56339E−06 A10 = −2.28093E−07,A12 = −1.28148E−08, A14 = 3.13084E−09 Surface No. 18 K = 0.00000E+00, A4= 1.90160E−04, A6 = 8.06372E−05, A8 = 5.02360E−06 A10 = −1.29991E−06,A12 = 0.00000E+00, A14 = 0.00000E+00 Surface No. 20 K = 0.00000E+00, A4= −3.85673E−04, A6 = 1.93928E−05, A8 = −8.23950E−07 A10 = 4.98393E−09,A12 = 0.00000E+00, A14 = 0.00000E+00 Surface No. 22 K = 0.00000E+00, A4= 1.33733E−03, A6 = −8.40850E−05, A8 = 5.21020E−06 A10 = −1.89946E−07,A12 = 2.92945E−09, A14 = 0.00000E+00 Surface No. 23 K = 0.00000E+00, A4= 1.25012E−03, A6 = −9.34022E−05, A8 = 5.55813E−06 A10 = −2.00544E−07,A12 = 3.06426E−09, A14 = 0.00000E+00

TABLE 12 (Various data) Zooming ratio 9.39473 Wide-angle MiddleTelephoto limit position limit Focal length 4.6466 14.2428 43.6536F-number 3.08881 4.92645 5.98483 View angle 41.5422 15.0391 5.0055 Imageheight 3.6000 3.9000 3.9000 Overall length 42.4542 46.6111 55.6771 oflens system BF 0.77933 0.75151 0.73920 d6 0.3000 7.6536 17.9500 d1216.4289 6.0700 0.9031 d19 1.0129 6.9323 10.8336 d21 2.4853 3.9951 5.9037d23 4.7679 4.5287 2.6676 Entrance pupil 11.0513 25.3144 75.1476 positionExit pupil −11.4768 −31.6472 −99.8114 position Front principal 13.936233.2959 99.8492 points position Back principal 37.8076 32.3683 12.0235points position Single lens data Lens Initial surface element numberFocal length 1 1 −69.2986 2 3 50.3333 3 5 42.7195 4 7 −7.1113 5 9−15.8467 6 11 15.7790 7 13 7.5057 8 15 9.5156 9 17 −5.3467 10 20−47.2491 11 22 18.2151 Zoom lens unit data Initial Overall Lens surfaceFocal length of Front principal Back principal unit No. length lens unitpoints position points position 1 1 35.53500 4.46660 0.95744 2.62125 2 7−7.38792 5.12640 −0.01273 0.71601 3 13 10.21334 4.12050 −2.05831 0.067714 20 −47.24910 0.50000 1.07343 1.25927 5 22 18.21508 1.68640 0.660661.26673 Magnification of zoom lens unit Lens Initial Wide-angle MiddleTelephoto unit surface No. limit position limit 1 1 0.00000 0.000000.00000 2 7 −0.28399 −0.39590 −0.88325 3 13 −0.56572 −1.19853 −1.46846 420 1.26345 1.28209 1.24347 5 22 0.64419 0.65885 0.76170

Numerical Example 5

The zoom lens system of Numerical Example 5 corresponds to Embodiment 5shown in FIG. 13. Table 13 shows the surface data of the zoom lenssystem of Numerical Example 5. Table 14 shows the aspherical data. Table15 shows various data.

TABLE 13 (Surface data) Surface number r d nd vd Object surface ∞  147.82760 0.75000 1.84666 23.8  2 28.21300 0.01000 1.56732 42.8  328.21300 3.27700 1.49700 81.6  4 −1107.87480 0.15000  5 25.29660 2.383001.72916 54.7  6 77.85170 Variable  7 64.54210 0.30000 1.88300 40.8  85.72810 2.90780  9 −28.89180 0.30000 1.78590 43.9 10 16.49550 0.41550 1111.41710 1.41500 1.94595 18.0 12 54.34020 Variable 13 6.03730 3.329601.49700 81.6 14 −48.63350 0.93260 15* 12.17690 3.24180 1.80470 41.0 16−40.55760 0.01000 1.56732 42.8 17 −40.55760 0.40000 1.84666 23.8 187.33790 0.30000 19(Diaphragm) ∞ Variable 20* 10.70960 1.79450 1.5250070.3 21* 682.87650 Variable 22 ∞ 0.78000 1.51680 64.2 23 ∞ (BF) Imagesurface ∞

TABLE 14 (Aspherical data) Surface No. 15 K = 0.00000E+00, A4 =−7.18404E−04, A6 = −2.38605E−05, A8 = −8.22730E−07 A10 = 0.00000E+00Surface No. 20 K = 0.00000E+00, A4 = −1.44429E−04, A6 = 3.93254E−06, A8= 3.07661E−07 A10 = −1.38658E−08 Surface No. 21 K = 0.00000E+00, A4 =−1.01717E−04, A6 = 2.13630E−06, A8 = 4.46802E−07 A10 = −1.80129E−08

TABLE 15 (Various data) Zooming ratio 13.97837 Wide-angle MiddleTelephoto limit position limit Focal length 4.6500 17.4002 64.9995F-number 3.58003 5.47052 6.27507 View angle 40.7265 12.6564 3.3680 Imageheight 3.5000 3.9020 3.9020 Overall length 51.3024 58.0531 68.9684 oflens system BF 0.90480 0.89076 0.84139 d6 0.3050 13.1596 25.0706 d1219.0154 5.8493 1.3032 d19 5.3359 5.8777 14.8307 d21 3.0445 9.5789 4.2257Entrance pupil 12.8525 47.1928 195.5208 position Exit pupil −11.9076−19.4587 −57.9755 position Front principal 15.8148 49.7147 188.6883points position Back principal 46.6524 40.6529 3.9688 points positionSingle lens data Lens Initial surface element number Focal length 1 1−82.7025 2 3 55.4103 3 5 50.4274 4 7 −7.1360 5 9 −13.3223 6 11 15.0389 713 11.0291 8 15 11.9660 9 17 −7.3110 10 20 20.7050 Zoom lens unit dataInitial Overall Lens surface Focal length of Front principal Backprincipal unit No. length lens unit points position points position 1 139.45012 6.57000 1.49757 3.93043 2 7 −6.77455 5.33830 0.19148 1.10718 313 11.56553 8.21400 −3.65554 1.57167 4 20 20.70503 1.79450 −0.018730.60013 Magnification of zoom lens unit Lens Initial Wide-angle MiddleTelephoto unit surface No. limit position limit 1 1 0.00000 0.000000.00000 2 7 −0.22934 −0.40603 −1.41907 3 13 −0.70721 −2.63780 −1.72585 420 0.72674 0.41182 0.67275

The following Table 16 shows the corresponding values to the individualconditions in the zoom lens systems of the numerical examples.

TABLE 16 (Values corresponding to conditions) Numerical ExampleCondition 1 2 3 4 5 (1) f₁/f₂ −6.20 −5.40 −6.40 −4.81 −5.82 (a)f_(T)/f_(W) 14.71 11.03 16.47 9.39 13.98 (2) |f₁/f₄| 2.81 3.76 2.30 0.751.91 (3) L_(T)/f_(T) 0.96 1.08 0.96 1.28 1.06

The present disclosure is applicable to a digital input device such as adigital camera, a mobile terminal device such as a smart-phone, aPersonal Digital Assistance, a surveillance camera in a surveillancesystem, a Web camera or a vehicle-mounted camera. In particular, thepresent disclosure is suitable for a photographing optical system wherehigh image quality is desired like in a digital camera.

As described above, embodiments have been described as examples of artin the present disclosure. Thus, the attached drawings and detaileddescription have been provided.

Therefore, in order to illustrate the art, not only essential elementsfor solving the problems but also elements that are not necessary forsolving the problems may be included in elements appearing in theattached drawings or in the detailed description. Therefore, suchunnecessary elements should not be immediately determined as necessaryelements because of their presence in the attached drawings or in thedetailed description.

Further, since the embodiments described above are merely examples ofthe art in the present disclosure, it is understood that variousmodifications, replacements, additions, omissions, and the like can beperformed in the scope of the claims or in an equivalent scope thereof.

What is claimed is:
 1. A zoom lens system, in order from an object sideto an image side, comprising: a first lens unit having positive opticalpower; a second lens unit having negative optical power; a third lensunit having positive optical power; a fourth lens unit having opticalpower; and an aperture diaphragm provided between the third lens unitand the fourth lens unit, wherein in zooming from a wide-angle limit toa telephoto limit at the time of image taking, the first lens unit, thesecond lens unit, and the third lens unit are moved along an opticalaxis to perform magnification change, the third lens unit includes twoor more lens elements, and one or more inter-lens-element air spaces,and the following conditions (1) and (a) are satisfied:−7.0<f ₁ /f ₂<−4.0  (1)f _(T) /f _(W)>9.0  (a) where, f₁ is a composite focal length of thefirst lens unit, f₂ is a composite focal length of the second lens unit,f_(W) is a focal length of the entire system at a wide-angle limit, andf_(T) is a focal length of the entire system at a telephoto limit. 2.The zoom lens system as claimed in claim 1, wherein in zooming from awide-angle limit to a telephoto limit at the time of image taking, theaperture diaphragm A moves along the optical axis, integrally with thethird lens unit.
 3. The zoom lens system as claimed in claim 1, whereinthe following condition (2) is satisfied:0.5<|f ₁ /f ₄|<4.2  (2) where, f₁ is a composite focal length of thefirst lens unit, and f₄ is a composite focal length of the fourth lensunit.
 4. The zoom lens system as claimed in claim 1, wherein thefollowing condition (3) is satisfied:0.8<L _(T) /f _(T)<1.4  (3) where, L_(T) is an overall length of lenssystem (a distance from a most object side surface of the first lensunit to an image surface) at a telephoto limit, and f_(T) is a focallength of the entire system at a telephoto limit.
 5. The zoom lenssystem as claimed in claim 1, wherein the fourth lens unit has negativeoptical power.
 6. The zoom lens system as claimed in claim 1, whereinthe fourth lens unit is composed of one lens element.
 7. An imagingdevice capable of outputting an optical image of an object as anelectric image signal, comprising: a zoom lens system that forms theoptical image of the object; and an image sensor that converts theoptical image formed by the zoom lens system into the electric imagesignal, wherein the zoom lens system is a zoom lens system as claimed inclaim
 1. 8. A camera for converting an optical image of an object intoan electric image signal, and performing at least one of displaying andstoring of the converted image signal, comprising: an imaging deviceincluding a zoom lens system that forms the optical image of the object,and an image sensor that converts the optical image formed by the zoomlens system into the electric image signal, wherein the zoom lens systemis a zoom lens system as claimed in claim
 1. 9. The zoom lens system asclaimed in claim 1, wherein a fifth lens unit having optical power isprovided on the image side relative to the fourth lens unit.
 10. Thezoom lens system as claimed in claim 9, wherein the fifth lens unit haspositive optical power.
 11. The zoom lens system as claimed in claim 9,wherein the fifth lens unit is composed of one lens element.
 12. Thezoom lens system as claimed in claim 9, wherein in focusing from aninfinity in-focus condition to a close-object in-focus condition, thefourth lens unit or the fifth lens unit moves along the optical axis.